Threaded fastener grades (Part 3

Order Reprints


Performance aftermarket fastener manufacturers offer much higher tensile strength fasteners that are specifically designed for racing applications. ARP, for example, offers threaded fasteners that boast 170,000 psi, 190,000 psi and 220,000 psi. In other words, instead of hitting the local hardware store or Internet source for imported who-knows-what-or-where-they-came-from fasteners, stick with reputable U.S. firms that are dedicated to supplying pro race engine and car builders.

Be aware that a lot of overseas junk is floating around out there, some of it counterfeit (low grade junk marked as Grade 8, etc.). If you want to screw on a dash plaque, feel free to grab whatever works. When it comes to stainless-steel fasteners, you can get burned very easily if you opt to buy unknown brand fasteners. The alloy mix is critical in terms of fastener strength.

If you want stainless stuff, buy only known performance fastener brands (again, ARP is but one example). They’ve selected the proper grade of stainless for specific automotive applications that will provide the performance and durability required. Buying generic stainless-steel fasteners can result in major grief down the road. When you’re building an engine or are about to assemble a chassis, don’t take chances. Know what you’re buying![PAGEBREAK]


18-8……………..Excellent corrosion resistance. Rockwell hardness B70. Minimum tensile strength 70,000 psi. Just a step above Grade 2 steel in terms of strength.
Type 316………..Better corrosion resistance (alloy contains moly). Minimum Rockwell hardness B70. Minimum tensile strength 70,000 psi.
Type 400………..Lower corrosion resistance but slightly stronger. Contains more carbon than 18-8 or 316. Minimum Rockwell hardness C28. Minimum tensile strength 75,000 psi.
ASTM F594 18-8 and Type 316….Same as 18-8 and 316 but meets strict ASTM standards.
ASTM A194 Grade 8M strain-hardened Type 316………Minimum Rockwell hardness C34. Minimum tensile strength 90,000 psi. Slightly greater strength than Grade 2 steel.
Alloy 20……..Also called carpenter 20. Most resistant to stress corrosion and high-temperature sulfuric acid. Rockwell hardness B89. Minimum tensile strength 85,000 psi.


Galvanic corrosion occurs when dissimilar metals are in contact with one another. Especially in salt water conditions, a small electrical current flows from one metal to another. One metal will begin corroding faster than normal, acting as the anode, and the other metal will corrode more slowly than normal (acting as the cathode). The result is that the anode material will corrode much faster than the cathode material. Galvanic corrosion can be avoided by using only similar metals (e.g., steel bolt in steel components, or aluminum bolts in aluminum components). Also, by using stainless-steel nuts on stainless-steel bolts, steel nuts on steel bolts, etc. However, we all know that in some cases, dissimilar metals will be assembled (installing stainless-steel nuts on steel bolts, etc.). In order to avoid galvanic corrosion (sometimes called electrolysis), apply a small amount of moly anti-seize compound or thread-locking compound to the threads before assembly to act as an insulator between the two metals.

Grade 8 steel bolt. Eight radial markings identify a grade 8 bolt, which should feature a minimum 150,000 psi tensile strength.

L9 (Grade 9) steel bolt. Rated at 180,000 psi tensile strength. These bolts feature a slightly taller-than-normal head thickness. A series of nine radial marks accompany the L9 mark.[PAGEBREAK]

Grade 8.8 metric steel bolt. This features a minimum tensile strength of 116,030 psi. In terms of strength, a metric 8.8 is roughly equivalent to a Grade 8 inch-format bolt.

Grade 10.9 metric steel bolt. In terms of strength, this is roughly equivalent to a Grade 8 inch-format bolt.

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